Why Does RawTherapee Apply a Different Flat-Field Correction to My Next Product Photograph?

Identify the reference selected for each photograph

Flat-field correction compensates for spatial nonuniformity recorded by a camera and lens. A flat-field reference describes the response of a particular capture configuration, not an arbitrary brightness gradient that should be imposed on every photograph.

RawPedia documents automatic selection based on camera and lens information, focal length, aperture and capture time. The closest available reference can therefore differ between two product photographs. A copied processing profile may preserve the instruction to use automatic selection without guaranteeing the same reference file.

Begin with two original RAW photographs. Record the camera, lens, focal length, aperture and capture date or time from their metadata. Inspect the flat-field files available to RawTherapee and identify which reference is selected for each photograph.

If the photographs use different optical settings, a different reference may be appropriate. If their metadata is identical but the selection differs, investigate reference availability, timestamps and the actual selection configuration before changing exposure or color controls.

Separate an incorrect match from an unsuitable reference

Compare the reference's capture configuration with the product image. A flat field made at another zoom position may describe different optical shading. An old reference may also be unsuitable if the camera or optical configuration changed.

Inspect the uncorrected RAW and the corrected result at the same viewing scale. Look for corner brightness, spatial color gradients and unintended changes to the product's pale surfaces.

If automatic selection chooses a reference that does not represent the capture conditions, test a deliberately selected appropriate flat field. If the available references do not cover the configuration, capture suitable calibration material instead of selecting an unrelated file merely to obtain a visually flatter background.

RawPedia also identifies special handling considerations for unusual tilt-shift configurations. Do not assume ordinary metadata matching fully describes a shifted optical arrangement.

Hypothetical zoom-lens catalog session

Hypothetical illustration—not an executed RawTherapee test: a merchant photographs a white cosmetic carton at 35 mm and a second carton at 70 mm using the same camera and zoom lens. Both files receive a shared profile configured for automatic flat-field selection.

The calibration folder contains FF-35 and FF-70, references intended for the corresponding focal-length configurations. The proposed review records which file RawTherapee actually selects rather than assuming the profile fixes one reference.

If the 70 mm photograph selects FF-35, the merchant checks whether FF-70 is available and whether its metadata permits a suitable match. If each photograph selects its corresponding reference but the white backdrop remains uneven, investigate the reference quality and physical lighting separately.

No actual selection outcome or correction quality is claimed.

Keep calibration identity in the batch record

For every approved source, record the RAW filename, relevant capture metadata, selected flat field and processing-profile version. Preserve the calibration files alongside the production record.

Do not use an apparently uniform background as the sole pass condition. Check that the product's actual color and surface shading remain supported by the original capture.

When a batch contains materially different optical configurations, divide it into appropriate calibration groups. Reprocess a representative image after changing the reference selection and compare the actual output before applying the change broadly.

The final decision is whether each photograph received a suitable capture-specific correction, not whether every photograph used the same file.

Record your own observations

The filled rows are illustrative examples. Use the blank row for your own files and observations.

Download the editable CSV worksheet

What the references establish

• RawPedia — Flat-Field: Documents automatic flat-field matching using camera and lens information, focal length, aperture and capture time, including closest-match behavior and unusual optical configurations.